A following patch adds fake overlay inodes, which are hashed by the same
real inode as an overlay inode or a trap inode.  Pass a key with the real
inode and the kind of inode to ovl_inode_test() and ovl_inode_set(), so
that all lookups share one test function.

No functional change intended.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
 fs/overlayfs/inode.c     | 57 ++++++++++++++++++++++++++++++++++++++----------
 fs/overlayfs/overlayfs.h |  5 +++++
 2 files changed, 51 insertions(+), 11 deletions(-)

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 5895ee5aa771..88cec47d0bc8 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -1069,17 +1069,50 @@ struct inode *ovl_new_inode(struct super_block *sb, umode_t mode, dev_t rdev)
 	return inode;
 }
 
+/*
+ * An overlay inode is hashed by a real inode.  A real inode can have a fake
+ * overlay inode next to its overlay inode or its trap inode.
+ */
+struct ovl_inode_key {
+	struct inode *real;
+	bool fake;
+};
+
 static int ovl_inode_test(struct inode *inode, void *data)
 {
-	return inode->i_private == data;
+	struct ovl_inode_key *key = data;
+
+	return inode->i_private == key->real &&
+	       ovl_test_flag(OVL_FAKE, inode) == key->fake;
 }
 
 static int ovl_inode_set(struct inode *inode, void *data)
 {
-	inode->i_private = data;
+	struct ovl_inode_key *key = data;
+
+	inode->i_private = key->real;
+	if (key->fake)
+		ovl_set_flag(OVL_FAKE, inode);
 	return 0;
 }
 
+static struct inode *ovl_ilookup(struct super_block *sb, struct inode *real,
+				 bool fake)
+{
+	struct ovl_inode_key key = { .real = real, .fake = fake };
+
+	return ilookup5(sb, (unsigned long)real, ovl_inode_test, &key);
+}
+
+static struct inode *ovl_iget_locked(struct super_block *sb, struct inode *real,
+				     bool fake)
+{
+	struct ovl_inode_key key = { .real = real, .fake = fake };
+
+	return iget5_locked(sb, (unsigned long)real, ovl_inode_test,
+			    ovl_inode_set, &key);
+}
+
 static bool ovl_verify_inode(struct inode *inode, struct dentry *lowerdentry,
 			     struct dentry *upperdentry, bool strict)
 {
@@ -1123,7 +1156,7 @@ struct inode *ovl_lookup_inode(struct super_block *sb, struct dentry *real,
 {
 	struct inode *inode, *key = d_inode(real);
 
-	inode = ilookup5(sb, (unsigned long) key, ovl_inode_test, key);
+	inode = ovl_ilookup(sb, key, false);
 	if (!inode)
 		return NULL;
 
@@ -1142,7 +1175,7 @@ bool ovl_lookup_trap_inode(struct super_block *sb, struct dentry *dir)
 	struct inode *trap;
 	bool res;
 
-	trap = ilookup5(sb, (unsigned long) key, ovl_inode_test, key);
+	trap = ovl_ilookup(sb, key, false);
 	if (!trap)
 		return false;
 
@@ -1166,8 +1199,7 @@ struct inode *ovl_get_trap_inode(struct super_block *sb, struct dentry *dir)
 	if (!d_is_dir(dir))
 		return ERR_PTR(-ENOTDIR);
 
-	trap = iget5_locked(sb, (unsigned long) key, ovl_inode_test,
-			    ovl_inode_set, key);
+	trap = ovl_iget_locked(sb, key, false);
 	if (!trap)
 		return ERR_PTR(-ENOMEM);
 
@@ -1218,12 +1250,15 @@ static bool ovl_hash_bylower(struct super_block *sb, struct dentry *upper,
 }
 
 static struct inode *ovl_iget5(struct super_block *sb, struct inode *newinode,
-			       struct inode *key)
+			       struct inode *real)
 {
-	return newinode ? inode_insert5(newinode, (unsigned long) key,
-					 ovl_inode_test, ovl_inode_set, key) :
-			  iget5_locked(sb, (unsigned long) key,
-				       ovl_inode_test, ovl_inode_set, key);
+	struct ovl_inode_key key = { .real = real };
+
+	if (!newinode)
+		return ovl_iget_locked(sb, real, false);
+
+	return inode_insert5(newinode, (unsigned long)real, ovl_inode_test,
+			     ovl_inode_set, &key);
 }
 
 struct inode *ovl_get_inode(struct super_block *sb,
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index d3a897e46ccb..f884e6695d2c 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -66,6 +66,11 @@ enum ovl_inode_flag {
 	OVL_CONST_INO,
 	OVL_HAS_DIGEST,
 	OVL_VERIFIED_DIGEST,
+	/*
+	 * A fake inode: not the overlay inode or the trap inode of the real
+	 * inode that it is hashed by.
+	 */
+	OVL_FAKE,
 };
 
 enum ovl_entry_flag {

-- 
2.55.0